Synthetic or natural latex gloves providing enhanced gripping characteristics are known to be extremely desirable, since they provide slip-resisting, gripping action, even when wet articles are handled. The external surface of the glove can be textured in order to obtain superior gripping properties. Traditional approaches include the use of textured formers, which are dipped into an aqueous latex emulsion resulting in a textured glove surface at the textured former contact surface. When the glove is inverted, the external glove surface becomes textured with a pattern representative of that on the former. Generally, the former external surface can be textured or indented in each of the finger, thumb tips, and body portions so that gloves with texture in these regions can be produced. The details of the texture produced can vary according to the requirements of the glove manufacturer. Unfortunately, this simple approach has limited applications, since dipping defects occur at the edges defining the texture, resulting in a latex film, which has holes or which tears easily at these defective regions. The textured former surface also readily degrades, and latex articles are difficult to strip from the former after cross-linking of the latex film, due to the texture present at the former-latex interface. The stripping action can tear formed latex articles or, in the worst case, produce pinholes and other defects, which may be difficult to observe but nevertheless deteriorate the overall quality and reliability of the latex product. For example, U.S. Pat. No. 6,081,928 and Int'l Pat. App. Pub. No. WO 00/19847 to Bourne discloses an elastomeric glove with enhanced grip strength. The gripping surfaces of the glove, preferably each of the finger and thumb tips and the body portions are molded with a plurality of concave indentations between 0.004 and 0.020 inches or with a plurality of suction cups with a circular border diameter ranging from 0.008 to 0.5 inches. The manufacturing process employs glove-dipping formers having surfaces comprised of a plurality of convex protrusions or suction cup structures. In another example, U.S. Pat. No. 6,254,947 to Schaller discloses flexible plastic articles bearing polymeric slip coatings and having raised/recessed roughness on their surfaces. This slip coating is comprised of a polymeric material and, at least in sections, has repeating shape deviations of the surface that are recessed in relation to a raised, net-like structure. The glove is made by dipping a porcelain former with a series of indentations, and the contacted surface becomes the external surface having protrusions, while the non-contact surface with recesses becomes the skin-contact surface and receives the soft polymeric coating. In a third example, U.S. Pat. No. 5,098,755 to Tanquary et al. discloses textured thermoplastic elastomeric film, articles comprising the same, and a method of making such a film and articles. Textured and embossed films for condom articles are provided with an embossed pattern with 1,000 to 100,000 embossments per square inch of embossed surface. Dipping a latex article does not form this texture, but the embossed pattern is formed by elevated heat and/or pressure-forming conditions. Heating of latex to produce an embossed pattern generally degrades its mechanical and barrier properties.
Another approach is to produce a rough gripping surface of a glove by foaming the latex external surface. Incorporating air into the aqueous latex produces this foamed surface. Air bubbles in latex generally are spherical in shape with non-uniform bubble sizes, due to the inherent instability resulting from larger bubbles growing when they contact smaller bubbles. When air bubbles touch each other, they form a much larger foam cell, and the roughness produced is not well-controlled. For example, U.S. Pat. No. 2,393,298 to De Laney discloses rubber glove and like articles. The former is dipped first in an aqueous latex emulsion, followed by a coagulant dip to harden the first latex layer, and then dipped in a foamed second latex layer, which is dipped in aerated runny latex, and the air bubbles burst to form a porous second layer. The former is then dipped in a coagulant layer to harden and stabilize the second foamed latex layer. In a second example, U.S. Pat. No. 4,589,940 to Johnson discloses a method of making foamed, slip-resistant surfaces. The surface of the gloves provides a porous, foam surface, so that the gloves are breathable and have moisture-absorbing properties. The porous latex foam is applied to a woven or non-woven substrate. Since the substrate is porous and the foamed latex is porous (40-95% porosity), the glove thus formed is breathable. The foam is stated to be abrasion-resistant and to provide improved gripping action. In a third example, U.S. Pat. No. 4,497,072 to Watanabe discloses a porous, coated glove. The porous glove is made of a fabric material with a coating layer that has sharp projections in the shape of broken bubbles, thereby providing tenacious gripping properties. The fabric glove base is formed from knitted fabrics, woven fabrics, or staple fiber materials. The fabric is then coated with a latex foaming solution, which is solvent-based. The process of evaporation of the solvent is assisted by reduced pressure, which breaks the air bubbles, forming sharp edges. Multiple bubbles can collapse together, as shown in FIGS. 3 and 4, resulting in uncontrolled texture of the glove surface. In a fourth example, U.S. Pat. No. 6,527,990 to Yamashita et al. discloses a method for producing a rubber glove. A rubber glove is produced by sequentially immersing a glove mold, first in a coagulating, synthetic rubber latex containing thermally expansible microcapsules and blowing agents. Next, it is immersed in a rubber-incorporating latex to form a gelled rubber layer forming a rubber laminate. The rubber laminate is then heated to vulcanize the rubber laminate, and to expand the microcapsules and blowing agents creating a foam. The laminate is turned inside out with the expanded microcapsule side forming the outer surface of the glove. This method produces a rubber glove, which is excellent in anti-blocking properties (no stickiness between two contacting gloves) and grip under dry or wet conditions, by a simple procedure and for a low cost.
Another approach for texturing latex gloves is to incorporate water-soluble particles in an uncured latex layer. For example, Japanese patent JP1258917 to Kishi discloses an uneven surface skin, for example, rubber glove obtained by adhering solid granular material on unsolidified resin emulsion latex and solidifying. A latex composition coating is formed on the surface of a mold. Under the state that the latex coating is still unsolidified, particulates, which do not dissolve in latex and which dissolve in water solution, such as salt, are scattered and adhered onto the latex coating. After the coating is vulcanized, the salt is removed by being washed with water in order to obtain rubber gloves made of non-air-permeable and non-water-permeable rubber skin with fine recessed or projecting parts on their surfaces. Since the latex is still fluid prior to vulcanization, the incorporated particles are covered by latex and are not easily dissolved to produce the desired surface structure. In a second example, U.S. Pat. No. 2,997,746 to O'Brien et al. discloses a method of making a roughened rubber product. The process uses insoluble hydrophilic solids in a non-aqueous medium, such as naphtha and other hydrocarbon solvents that essentially dissolve rubber. This rubber cement has added hydrophilic solids, such as sugar or salt, and, therefore, forms a latex coating with embedded hydrophilic solids on the former, when dipped, and the hydrophilic solids are dissolved in soapy water creating a roughened surface. Note that the hydrophilic solid employed is insoluble in naphtha or other hydrocarbon solvents employed to dissolve rubber. Sugar has a specific gravity of approximately 1.4, and salt has a specific gravity of 2.165. The latex solvent solution has a specific gravity of less than 1, depending upon the choice of solvents. The hydrophilic solids are not easily suspended in the latex solvent solution, due to the settling behavior of hydrophilic solids, especially when the solid size is large. Vigorous agitation is needed to suspend the hydrophilic solids in the latex solvent solution. When a form is dipped in this latex solvent solution, it may not receive uniform distribution of hydrophilic solids due to this settling behavior, and high levels of agitation in the latex solvent solution tend to knock away any particles that are incorporated. Further, the particle is not held in place until the solvent is dried, and only a few rapidly moving particles will be captured in the latex layer formed on the former, thus producing a sparsely textured, dipped article with poor texture uniformity. The swelling of the hydrophilic solids results in voids that are much larger than the solids added to the latex cement solution and may be even larger due to solvent evaporation, resulting in voids that are essentially devoid of any shape. These voids may also combine or coalesce to form even larger voids that are much larger than the starting sugar crystals. O'Brien does not disclose nitrile rubber compositions, since solvents for nitrile rubber are not readily available.
Several other disclosures related to grip-enhancing gloves are described in U.S. Pat. No. 6,675,392 to Albert and U.S. Pat. Nos. 6,745,403 and 6,526,593 to Sajovic. They relate to a method of obtaining grip for sporting gloves by installing plastic suction cup-shaped devices onto the gloves. These features are attached later to the glove surface, are not an integral part of the glove, and provide grip in limited areas of the glove appropriate for the sporting purpose intended. These suction cups do not provide overall gripping.
There remains a need in the art for latex articles and glove surfaces that are textured and provide superior gripping properties when handling dry, wet or oily objects. The external surface of the glove must have an engineered surface, preferably with a well-designed, reproducible texture of geometrical features that assist in eliminating the fluid boundary layer between the glove's external surface and that of the object being gripped. There remains a need for a reliable process for the creation of this engineered, external textured glove surface that requires complete control of the size, the shape and the distribution of the surface features of a latex glove formed by the most commonly used industrial process of latex in-line dip processing. It is an object of the present invention to provide such latex articles and glove surfaces, as well as a process for making the same. These and other objects and advantages, as well as additional inventive features, will become apparent from the detailed description provided herein.